The present invention relates to a reactor for making hydrogen cyanide and sodium cyanide. The present reactor is using a process that is an improvement over the previously known Andrussow process for making hydrogen cyanide (HCN) and sodium cyanide (NaCN). In particular, the reactor according to the invention is using a process relating to improvement of the efficiency of the new process (hereafter called the new process) compared to the Andrussow process.
The invention thus in one embodiment relates to a reactor for converting methane, ammonia and oxygen and alkaline or alkaline earth hydroxides into alkaline or alkaline earth cyanides by two-stage reactions;
1—a catalytic reaction process over a catalyst material between ammonia, methane and oxygen wherein hydrogen cyanide, carbon monoxide/dioxide and water are formed, wherein the reaction gases are mixed, and
2—the gases being cooled prior to being absorbed with an alkaline or alikaline earth hydroxide for producing a corresponding cyanide, wherein the reactor comprises a first stage with a gas inlet, wherein the first stage is formed by a cone with distribution plates providing an even gas distribution over the catalyst material, wherein the distribution plates are located between the gas inlet of the reactor and a catalyser basket within the reactor located beneath the distribution plates, the distribution plates and being perforated with a number of holes with a diameter less than 20 mm and with a pitch larger than 1 diameter, with the distribution plates spaced from each other in the flow direction of the gas, the first distribution plate(s) functioning mainly to distribute the gas whereas the last distribution plate works as a heat radiation shield and as a distribution plate facing the catalyst gauze, and wherein the catalyst gauze is present in the form of catalyst gauze(s) fixed by catalyst weights.
Hydrogen cyanide (HCN) is one of the smaller volume industrial chemicals, which nevertheless is quite important in the chemical industry. In particular, HCN is used for the manufacture of cyanuric chloride, methyl methacrylate, adiponitrile (for nylon-6,6), sodium cyanide, ferrocyanides and chelating agents. Sodium Cyanide is mainly used for the heap leaching of Gold (Au) and Silver (Ag).
At present, almost all of the world's production of HCN/NaCN is made by one of three processes:
(1) The Andrussow process in which ammonia, methane and oxygen are reacted over an oxidation catalyst to form HCN, CO, water and H2;
(2) The “methane-ammonia direct process” or Degussa process in which ammonia and methane are reacted in the absence of air in externally heated tubes containing platinum/rhodium catalyst to form HCN and hydrogen; and
(3) The Shawinigan process in which ammonia and propane are passed between spaced electrodes within a fluidized bed of coke. In addition to the above processes for making HCN directly, it is also made as a by-product in the manufacture of acrylonitrile by reaction of propylene and ammonia over an oxidation catalyst.
To produce NaCN, all different processes must absorb HCN with sodium hydroxide (NaOH).
Though each of these processes is used commercially, by far the most widely used is the Andrussow process. In the Andrussow process, a vapour phase mixture of oxygen-containing gas (usually air), ammonia (NH3) and methane is contacted with platinum metal catalyst at a temperature of about 1200° C. by which part of the methane is burned to furnish heat to the methane-ammonia reaction, which is endothermic. The overall reaction of the Andrussow process is as follows:CH4+NH3→HCN+3H2 CH4+NH3+3/2O2→HCN+3H2O2H2+O2→2H2OHCN+NaOH→NaCN+H2O
The overall reactions in the new process used in the reactor according to the present invention also include:CH4+O2→CO+H2O+H2 CH4+2O2→CO2+2H2ONH3+O2→NO+H2O+H2 NO+CO+3/2H2→HCNO+H2ONO+CO+3/2H2→HNCO+H2OHNCO+NaOH→NaCN+H2O+½O2 HCNO+NaOH→NaCN+H2O+½O2 
The above reactions used in the reactor according to the present invention is by way of example shown through the basic reaction of sodium hydroxide with HCN, HNCO and HCNO, but any alkaline or alkaline earth metal such as potassium, calcium, magnesium etc. may be used equally well.
One characteristic of the Andrussow process is that the catalyst becomes less active with use. Though the cause for such deactivation is not precisely known, it is believed to be in part due to the formation of carbon on the catalyst, which results in a blocking of part of the active sites on the catalyst surface with a thin layer of carbon. This deactivation of the active sites of the catalyst lowers the conversion of ammonia and methane to an average of around 65%.
Because of the higher cost of methane and ammonia, it is essential that available methane and ammonia sources be utilized in the most effective manner.